Endogenous digitalis-like substances(EDLS) or factors(EDLF) are putative substances which have been thought to be pathogens to hypertention and to possess cardiotonic activity through inhibiting of Na/K ATPase. Some of them seem to regulate natriuresis in kidney and those or the others of them seem to possess an unknown function in eyes, though recognized so far only as pathogens to cataract A lot of compounds have been reported as a substance of EDLF so far. Recently, a conclusion that EDLF was ouabain itself was reported by Hamlyn et al. However, it is still controversial if their ouabain is really endogenous, because it has been known that the digitalis activity derived from foods, especially vegitables, may accumulate in adrenal wherefrom it may be released into blood. Several years ago, Inagami et al reported their EDLF isolated from bovine adrenals possessed the molecular weight of 336. This fact, as well as several information by Grave et al, Bricker et al, and Goto et al, prompted us to deduce a structure for Inagami-Tamura's EDLF and thus lead us to a possible structure, (1). In order to reveal the structure more, we attempted to isolate a lot of amount of the EDLF from 92 kg of bovine adrenals. However, that work ended unsuccessfully. Thus, we decided to elucidate its structure through the repetetion of designing of a target molecule, synthesis, and biological evaluation. Target molecules, (26) and (29), synthesized through 17 steps from estradiol (2), showed the contractile activity on an isolated rat aorta and an isolated Guinea pig atrium. However, they were less potent than less oxygenated compounds, (30) and (31). (See Fig. 3,4,5,and 6.) These results suggest the structure (1) is substancially probable but a further study for a true character of the EDLF should be continued.